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| author | Jorropo <jorropo.pgm@gmail.com> | 2025-07-04 09:26:38 +0200 |
|---|---|---|
| committer | Gopher Robot <gobot@golang.org> | 2025-07-24 13:49:07 -0700 |
| commit | f32cf8e4b025eee84aa3ec690966fa4e737a7522 (patch) | |
| tree | 10470a3f9270c7767fff7c68c8740fe65a47bf96 /src | |
| parent | d574856482859d259a95826dea404e648cbb8fef (diff) | |
| download | go-f32cf8e4b025eee84aa3ec690966fa4e737a7522.tar.xz | |
cmd/compile: learn transitive proofs for safe unsigned subs
I've split this into it's own CL to make git bisect more effective.
Change-Id: I436ff21a3e2362b3924de25a458534eb9947e013
Reviewed-on: https://go-review.googlesource.com/c/go/+/685821
Reviewed-by: Keith Randall <khr@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>
Diffstat (limited to 'src')
| -rw-r--r-- | src/cmd/compile/internal/ssa/prove.go | 15 |
1 files changed, 15 insertions, 0 deletions
diff --git a/src/cmd/compile/internal/ssa/prove.go b/src/cmd/compile/internal/ssa/prove.go index cf045629cb..0c0581690f 100644 --- a/src/cmd/compile/internal/ssa/prove.go +++ b/src/cmd/compile/internal/ssa/prove.go @@ -2164,6 +2164,10 @@ func signedAddOverflowsOrUnderflows(a, b int64, t *types.Type) bool { } } +func unsignedSubUnderflows(a, b uint64) bool { + return a < b +} + func addLocalFacts(ft *factsTable, b *Block) { // Propagate constant ranges among values in this block. // We do this before the second loop so that we have the @@ -2226,6 +2230,17 @@ func addLocalFacts(ft *factsTable, b *Block) { } ft.update(b, v, v.Args[0], signed, r) } + case OpSub64, OpSub32, OpSub16, OpSub8: + x := ft.limits[v.Args[0].ID] + y := ft.limits[v.Args[1].ID] + if !unsignedSubUnderflows(x.umin, y.umax) { + r := lt + if !y.nonzero() { + r |= eq + } + ft.update(b, v, v.Args[0], unsigned, r) + } + // FIXME: we could also do signed facts but the overflow checks are much trickier and I don't need it yet. case OpAnd64, OpAnd32, OpAnd16, OpAnd8: ft.update(b, v, v.Args[0], unsigned, lt|eq) ft.update(b, v, v.Args[1], unsigned, lt|eq) |